Arc lamps are glass or quartz vessels that house electrodes that are used to produce an electrical arc for illumination purposes. The vessel is usually filled with a gas such as xenon or mercury. Sometimes various other elements are added to obtain an enhanced color temperature or the electrical arc such as sodium. The electrodes of the arc lamp are usually sealed by pinching the glass or quartz from the vessel around each electrode during a heat sealing process. The area where the electrodes have been sealed by the pinching process is commonly referred to as a “pinch”.
It is important during operation of the arc lamp that each pinch not be allowed to rise above a certain temperature. Allowable temperatures for the pinch range from three hundred degrees centigrade to four hundred and fifty degrees centigrade. If the temperature of a lamp pinch is allowed to rise over the highest operating temperature the pinched area can start to oxidize rapidly in the area where the sealing of the electrode takes place. The oxidization of the pinch area at the electrode causes a catastrophic seal leak and can cause the vessel to leak out the filler gas sometime resulting in an explosion. U.S. Pat. No. 3,377,498 to Koury et al describes a high pressure arc lamp, and is incorporated by reference herein. U.S. Pat. No. 3,723,784 to Sulcs et. al. is incorporated by reference herein, and describes a high pressure sodium lamp with “heat reflecting shields surrounding its electrodes”. Sulcs describes “Thus the seal temperature and the cold spot temperature can be controlled by adjusting the width of the foil”. U.S. Pat. No. 4,721,887 to Inukai et al, incorporated by reference herein, describes a method of creating a pinched arc lamp seal.
It has been found that direct radiation and reflected radiation emitted from the arc created by the arc lamp can be absorbed by the external electrode connecting leads. It is desirable to reduce the absorbed radiation of the external electrode connecting leads in order to reduce the temperature of the lamp pinch.